The objective of this proposal is to develop our recently achieved transformation of the Basidiomycete, Schizophyllum commune. This fungus has a well characterized set of mating-type genes that regulate development. These mating-type genes co-ordinate the expression of at least 30 nuclear genes. The molecular products of mating-type genes act as master regulatory switches that determine self- nonself recognition. A transformation system is essential to isolating the mating-type genes, isolating their products and identifying the mechanisms by which they regulate development. Once a transformation system is developed Schizophyllum will become an important model for studying self- nonself recognition. Recently we discovered a transformation system with great potential. Briefly, the TRPCF gene of Schizophyllum was isolated by complementation of trpC and F in E. coli. This gene was used to transform a Schizophyllum trpC mutant to trp+. These results show transformation of Schizophyllum is possible and is the first report of a functional transformation system in a Basidiomycete. The Specific Aims of this proposal are directed at improving the transformation system to the point where it becomes useful for isolating and studying mating-type genes. Work includes improving the transformation frequency, constructing vectors for cotransformation with TRPC, identifying other Schizophyllum genes by complementation in Schizophyllum, developing ways to recover genes from transformants, characterizing the integration of transforming DNA, and determining the structure of the TRPCF gene.